The invention relates to heat exchangers, and particularly, to heat exchangers for removing heat from high temperature gases, such as an exhaust gas.
Heat exchangers to remove heat from a stream of exhaust gas or other elevated temperature gas are well known. As one example known in the art, exhaust gas recirculation (EGR) coolers are used in combination with internal combustion engines operating on the Diesel or the Otto cycle (among others) to lower the temperature of a portion of the exhaust produced by the engine, so that that portion of the exhaust can be recirculated back to the air intake manifold of the engine. Such recirculation of exhaust gas is known to be effective in reducing the amount of a known pollutant (oxides of nitrogen) produced during the combustion process.
A typical EGR cooler of the kind described above is depicted in FIG. 1. The cooler 101 provides a flow path, extending from an exhaust inlet 102 to an exhaust outlet 103, for a stream of exhaust gas received from the engine. The exhaust gas is received into an inlet manifold 104 adjacent to the exhaust inlet 102, and is distributed to several fluid conveying tubes that extend from the inlet manifold 104 to a similar outlet manifold 105 arranged adjacent to the exhaust outlet 103. A casing 108 extends from the inlet manifold 104 to the outlet manifold 105 and provides a cooling water jacket surrounding the exhaust conveying tubes. Circuited cooling water is directed through the cooling water jacket by way of coolant ports 106 and 107, so that the exhaust gas traveling through the cooler 101 is reduced in temperature by the transfer of heat to the circuited cooling water.
While heat exchangers such as cooler 101 of FIG. 1 may be suitable for their intended purpose of cooling an exhaust gas, they are far from perfect. As one example, harsh mechanical stresses are often imposed on the heat exchanger by the cyclic thermal expansions and contractions that it experiences over its operational lifetime. These mechanical stresses can, at least in part, be the result of the differences in thermal expansion between the relatively cool casing 108 and the relatively hot fluid conveying tubes, and can lead to premature structural failure of the cooler 101 (e.g. a breach in the separation of the exhaust gas from the coolant). Thus, there is still room for improvement.